Oftentimes loyalty is in the eye of the beholder.
Everyone has different "expectations" of their family, friends, lovers, and spouse. Some people want you to dislike others simply because (they) don't get along with them! From their point of view you would be disloyal because you associate with them. Others expect people close to them to be willing to lie to the police or on a witness stand to keep them from going to jail.
Some people expect you to drop whatever you're doing and come to their rescue whether they're in a bar fight they initiated or in need of serious cash.
For others loyalty supersedes honesty!
They expect you to always take their side in any argument or disagreement regardless of the facts.
Lastly when it comes to romantic relationships most couples expect their mate to be monogamous and not maintain any "secret friendships". However cheating like loyalty is also in the eye of the beholder.
Too often people are quick to call something cheating BEFORE they're in an "exclusive relationship". The very essence of the word cheating is (breaking the rules). If a couple has yet to define their relationship as being "exclusive" than dating multiple people is not cheating.
Communication trumps assumption everyday of the week!
At the very basic level people want to know if they confide in you you will not tell others their secrets and you will uphold your promises.